The present invention relates to a feed unit, in particular for the feeding of fuel, the feed unit having an electric drive motor and a pump unit coupled to it, the pump unit comprising a first housing part having a first annular sector-shaped feed channel which debouches into an axial inlet opening, and a second housing part having a second annular sector-shaped feed channel of the same diameter as the first one debouching into an axial outlet opening. The pump unit includes a central passage opening for the drive shaft of the drive motor. A pump wheel which is functionally connected to the drive shaft is arranged between the two housing parts and has a plurality of tooth-shaped blades which are arranged in the circumferential region of the wheel and cooperate with the sector-shaped feed channels.
Feed units of this type are already known in which the two housing parts and the pump wheel of the pump unit consist of aluminum. The parts are produced by the metal injection molding process and, subsequently, anodized or hard-coated which makes the parts very expensive. These known feed units are used in motor vehicles for the injection of gasoline, a nominal pressure on the order of 1.5 bar being required. With reference to the highest possible efficiency, this rated pressure can only be achieved if the axial gaps between pump wheel and housing parts are as small as possible. There are desired axial gaps of a total of 3/100 mm. For this reason, such pump units cannot be manufactured of thermoplasts or duroplasts because these plastics in combination with fuel tend to swell and therefore, after a few hours, block the swollen pump wheel between the housing parts. For the manufacture of these parts, therefore, aluminum which can be processed by injection molding has gained acceptance. However, as already mentioned, the follow-up work which is indispensable for this material is disadvantageous and greatly increases the costs.
The efficiency of the pump unit furthermore depends decisively on the course of the annular channels and their surface roughness. The smaller the latter, the higher the efficiency. By using aluminum, very slight surface roughnesses can be obtained so that the use of aluminum has up-to-now been retained also for this reason.